This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. xc2xa7119 from an application for OPTICAL WAVELENGTH FILTER AND DEMULTIPLEXER earlier filed in the Korean Industrial Property Office on the Nov. 28th, 1996 and there duly assigned Ser. No. 59175/1996.
1. Technical Field
The present invention relates to an optical wavelength filter and an optical demultiplexer for a receiver of a wavelength division multiplexing (WDM) transmission system and, more particularly, to an optical wavelength filter and an optical demultiplexer for a low-loss, high-efficiency WDM transmission system.
2. Related Art
A WDM transmission system multiplexes the wavelength area of an optical fiber into several channels by simultaneously transmitting signals of several wavelength bands, relying on wavelength characteristics of an optical signal. In the WDM transmission system, an input optical signal, having been multiplexed so as to have several wavelength components, is demultiplexed at the receiver and recognized in the respective channels.
Typically, an optical demultiplexer for a receiver of a conventional WDM transmission system includes a coupler, that is, a passive device for branching an input channel into several output channels, and a plurality of band pass filters, one for each output channel, for passing respective wave length components of the output channel of the coupler. A substantial problem in the operation of such a demultiplexer resides in the fact that processing of the input optical signal in the coupler results in generation of a plurality of output optical signals, each of which is reduced in power by a factor proportional to the number of output channels of the coupler. As explained in more detail below, attempts have been made to compensate for this power loss (for example, by provision of an optical amplifier at the input side of the coupler), but such solutions are undesirable and have certain disadvantages. Therefore, there is a need in the prior art to provide an optical wavelength filter for reflection of an optical signal having a predetermined wavelength component without power loss, and to provide an optical demultiplexer for a receiver in an optical WDM transmission system providing little or minimal power loss.
The following patents are considered to be representative of the prior art relative to the present invention, and are burdened by the disadvantage discussed above: U.S. Pat. No. 5,657,406 to Ball, entitled Efficient Optical Wavelength Multiplexer/De-Multiplexer, U.S. Pat. No. 5,652,814 to Pan et al., entitled Integrable Fiberoptic Coupler And Resulting Devices And Systems, U.S. Pat. No. 5,627,925 to Alferness et al., entitled Non-Blocking Optical Cross-Connect Structure For Telecommunications Network, U.S. Pat. No. 5,615,290 to Harasawa et al., entitled Branch Device For Optical Multiplex System, U.S. Pat. No. 5,615,289 to Duck et al., entitled Bandpass Optical Filter, U.S. Pat. No. 5,608,825 to Ip, entitled Multi-Wavelength Filtering Device Using Optical Fiber Bragg Grating, U.S. Pat. No. 5,488,500 to Glance, entitled Tunable Add Drop Optical Filtering Method And Apparatus, U.S. Pat. No. 5,487,120 to Choy et al., entitled Optical Wavelength Division Multiplexer For High Speed, Protocol-Independent Serial Data Sources, U.S. Pat. No. 5,457,760 to Mizrahi entitled Wavelength Division Optical Multiplexing Elements, U.S. Pat. No. 5,448,390 to Tsuchiya et al., entitled Wavelength Division Multiplex Bothway Optical Communication System, U.S. Pat. No. 5,446,809 to Fritz et al., entitled All Fiber Wavelength Selective Optical Switch, U.S. Pat. No. 5,414,548 to Tachikawa et al., entitled Arrayed-Wave Guide Grating Multi/Demultiplexer With Loop-Back Optical Paths, U.S. Pat. No. 5,365,344 to Eda et al., entitled System For Transmitting Data Using Wavelength Division Multiplexing, and U.S. Pat. No. 4,923,271 to Henry et al., entitled Optical Multiplexer/Demultiplexer Using Focusing Bragg Reflectors.
It is an object of the present invention to provide an optical wavelength filter for reflecting an optical signal having a predetermined wavelength component without power loss.
It is another object of the present invention to provide an optical demultiplexer for a receiver in an optical WDM transmission system, which allows little power loss.
Accordingly, to achieve the above first object, there is provided an optical wavelength filter. The optical wavelength filter has a first optical device and a second optical device. The first optical device includes first, second and third ports, receives an input optical signal having a plurality of wavelength components, directs the input optical signal to the second port, and directs an optical signal returning from the second port only to the third port.
The second optical device includes fourth and fifth ports. The fourth port is connected to the second port of the first optical device. The second optical device reflects only an optical signal having a predetermined wavelength component in the optical signal received via the fourth port, and passes an optical signal having the other wavelength components to the fifth port.
To achieve the second object, there is provided an optical demultiplexer. The optical demultiplexer has a plurality of first optical devices and a plurality of second optical devices. Each of the first optical devices has first, second and third ports, receives an input optical signal via the first port, directs the input optical signal to the second port, and directs an optical signal returning from the second port only to the third port.
Each of the second optical devices has fourth and fifth ports which are connected between the second port of a corresponding first optical device and the first port of another corresponding first optical device, reflects only an optical signal having a predetermined wavelength component in an optical signal received via the fourth port backward from a light traveling direction, outputs the reflected optical signal to the corresponding first optical device via the second port thereof, and passes an optical signal having the other wavelength components to the other first optical device connected to the fifth port via the first port thereof.